JP3431751B2 - Combined differential detector - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical pickup detection system, and more particularly to a composite type differential detector applicable to a waveguide type optical pickup detection system, an object surface shape detection system and the like.

[0002]

2. Description of the Related Art In recent years, various studies have been made in various fields to reduce the size and cost of optical pickups for optical disk devices by integrating them on a single substrate with a waveguide.
One of them is the slab optical wav
As a structure for deflecting guided light guided in an eguide) by reflection, a waveguide type reflector is known in which a cross section perpendicular to the substrate is formed in the waveguide and reflected at this cross section. That is, when there is a difference in the refractive index of the medium, when the guided light is guided toward the medium boundary surface and the refractive index of the guided medium is larger than the refractive index of the medium ahead of the boundary surface, the so-called
The guided light can be reflected by total internal reflection. In addition to such properties, by giving a curvature to the boundary surface, guided light guided in the slab type optical waveguide can be condensed or diverged by reflection. That is, a waveguide reflection concentrator is formed by giving a curvature to the boundary surface.

As an optical pickup or a waveguide type optical signal detector utilizing such a technique, for example, there are those disclosed in Japanese Patent Laid-Open Nos. 3-192542 and 4-17133.

A waveguide type optical signal detection device constructed according to the slab type optical integrated pickup described in Japanese Patent Laid-Open No. 4-17133 will be described with reference to FIG.
First, a slab type optical waveguide 1 formed by sequentially laminating a buffer layer, a core layer and a clad layer on a silicon substrate is provided, and a prism coupler 2 having a triangular cross section is provided on one in-plane end side of the slab type optical waveguide 1. It is glued. The prism coupler 2 couples and guides external light, for example, reflected light from an optical disk, into the waveguide layer of the slab type optical waveguide 1. Waveguide-type reflection concentrators 3 and 4 that take in the respective guided lights and reflect and condense them are formed symmetrically. Here, these waveguide type reflection concentrators 3 and 4 reflect the reflective boundary surfaces 3a and 4a having a curvature for condensing and the condensed reflected light from the reflective boundary surfaces 3a and 4a. It is formed by a combination with the flat boundary surfaces 3b and 4b. Further, two photodetectors 5a, 5b, 6a, 6b which are bilaterally symmetric with respect to the optical axis of the condensed reflected light are provided at the focal positions of the condensed reflected light by the waveguide type reflection collectors 3, 4. Two-divided waveguide type photodetectors 5 and 6 respectively having the above are formed (specifically, formed on a silicon substrate).

In such a structure, for example, the slab type optical waveguide 1 is arranged so that the prism coupler 2 faces the objective lens, and the reflected light from the optical disk passes through the objective lens and the prism coupler 2. It is coupled and guided in the slab type optical waveguide 1. Now, assuming that the spot on the optical disk surface is in focus, the light coupled and guided to the slab type optical waveguide 1 via the prism coupler 2 becomes parallel light. In this case, the guided light is condensed and reflected by the waveguide type reflection collectors 3 and 4 arranged symmetrically about the optical axis in equal parts, and the condensed reflection light by the waveguide type reflection collector 3 is a photodetector. The light collected and reflected by the waveguide type reflection collector 4 is collected at the centers of the light detectors 6a and 6b. Therefore, when the outputs of the photodetectors 5a, 5b, 6a, 6b are Sa, Sb, Sc, Sd, the amounts of light incident on the photodetectors 5a, 5b are the same during focusing, and the difference signals between the two are detected. Sa-Sb becomes zero. The incident light amounts on the photodetectors 6a and 6b are the same, and the difference signal Sc-
Sd becomes zero.

However, when a defocused state occurs, the position of the condensed spot of the condensed reflected light by the waveguide type reflection collectors 3 and 4 is changed from the center of each of the two-divided waveguide type photodetectors 5 and 6. Moving. For example, when the optical disk position is close, the light receiving component outside the optical axis becomes large, so Sa>
Sb and Sc <Sd, and conversely, when the optical disc position is far, the light receiving component inside the optical axis becomes large, and therefore Sa <Sb and Sc> Sd. Therefore, (Sa
The focus error can be detected by detecting the positive / negative of + Sd)-(Sb + Sc). The tracking error signal ΔT is calculated as ΔT = (Sa + Sb) − (Sc + Sd). Furthermore, pit signal (reproduction signal RF)
Is calculated as, for example, RF = Sa + Sb + Sc + Sd.

[0007]

However, in the case of the device having the configuration shown in FIG. 7, even if the light coupled and guided to the slab type optical waveguide 1 via the prism coupler 2 is parallel light, The light collected and reflected by the type reflection collector 3 is not collected at the center of the photodetectors 5a and 5b, and the light collected by the waveguide reflection collector 4 is collected at the center of the photodetectors 6a and 6b at the same time. Then, since the focus error signal ΔF is not zero, it cannot be detected correctly. Therefore, when the focus positions of the waveguide type reflection concentrators 3 and 4 deviate due to an error in manufacturing the device, the offset cannot be adjusted. That is, in order to correct the focal position shift, the incident angle to this device is adjusted and the waveguide type reflection collector 3 on one side is adjusted.
Even if the offset can be completely removed for (or 4), the offset remains for the other waveguide type reflection concentrator 4 (or 3). As a result, the focus error signal ΔF cannot be normally detected as described above. Further, the track error signal ΔT can be obtained by taking the difference signal between the sum signal of the photodetectors 6a and 6b and the sum signal of the photodetectors 5a and 5b, but the response characteristic of the track error signal ΔT is the focus error signal ΔF. Will be slower than the response characteristics of.

Incidentally, when considered more generally with reference to the configuration shown in FIG. 7, for example, the two-division waveguide type photodetector 5 side is not divided into two photodetectors 5a and 5b. Type photodetector (tentatively referred to as single type photodetector 5) and combined with two-split waveguide type photodetector 6 (tentatively referred to as two-split type photodetector 6) to form a composite differential It can also be configured as a detector. By thus providing the single-type photodetector 5 and the two-division-type photodetector 6 having the two photodetectors 6a and 6b, the single-type photodetector 5 and the two-division-type photodetector are detected. To detect a certain state based on a difference signal between the photo detector 6 and another detector based on a difference signal between the two photo detectors 6a and 6b in the two-division photo detector 6 itself. Is possible. In this case, the response speed at the time of detecting a certain state based on the difference signal between the single-type photodetector 5 and the two-division-type photodetector 6, and the two lights in the two-division-type photodetector 6 itself. There is a demand for uniform response speeds when detecting another certain state based on the difference signal between the detectors 6a and 6b. For example, in measuring the surface shape of an object, when the information on the height and the gradient of the measurement point is simultaneously detected by using such a composite type differential detector, the detection processing of two pieces of information obtained from the measurement point is synchronized. It is desirable that it be good. Further, when the focus error signal and the track error signal are simultaneously detected by the composite type differential detector in the optical pickup, the suppression of the detection response speed deviation between the focus error signal and the track error signal stabilizes the servo control. It will be an important issue in planning. In particular, in recent years when the speed of reading and writing has been increasing, the importance of this problem tends to increase. However, even in the case of considering such a composite type differential detector, as in the case described with reference to FIG. 7, no measures are taken to align the detection response speed characteristics of a plurality of types of signals. Will become a device that requires complicated synchronization processing and the like.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide a composite type differential detector capable of aligning the detection response speed characteristics when simultaneously detecting a plurality of types of signals, and further, to further improve its detection range. An object is to provide a compound type differential detector that can be expanded.

[0010]

The invention according to claim 1 is
And a single optical detector, and a two-division photodetector having two optical detectors, for detecting the No. Sashin between these single photodetector and 2 division type optical detector together with the in composite differential detector to detect the issue Sashin between the two photodetectors in the two split photo detectors, and the light receiving portion of said single optical detector the two-divided type light The light receiving area ratio between the two photodetectors and the light receiving portions of the two photodetectors is approximately 1: 1: 1.
Is set to. Therefore, the light-receiving areas of the three light-receiving portions for the single-type photodetector and the two photodetectors forming the two-divided photodetector are substantially equal, and the response speed characteristics of these detectors are also substantially the same. , The signals obtained from these three photodetectors have no delay in response, and the response characteristics are uniform. Therefore, the complexity of synchronization processing between a plurality of types of signals is reduced. For example, when the servo control is applied to an optical pickup or the like based on a focus error signal or a tracking error signal, the timing error is reduced and the servo control can be stabilized.

According to the second aspect of the invention, the single type photodetector and the two-division type photodetector are formed in the slab type optical waveguide device in the vicinity of the surface on the waveguide layer side on the waveguide substrate.
Therefore, it is possible to increase the measurement range, which is difficult with the bulk type optical arrangement. Further, since the light-collecting element can be integrated into the waveguide element, the arrangement accuracy is improved and the arrangement adjustment is not required.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A first embodiment of the present invention will be described with reference to FIGS. First, the basic configuration and operation of this embodiment will be described with reference to FIG.

The composite type differential detector 11 of the present embodiment is
Single-type photodetector 12 and two photodetectors 13a and 13b
And a two-division type photodetector 13 having Here, the light receiving part of the single type photodetector 12 and the light receiving part 2
Two photodetectors 13a, 1 in the split photodetector 13
The ratio of the light receiving area to each light receiving portion of 3b is set to 1: 1: 1 (even if it is not strictly 1: 1: 1, it is about 1: 1: 1).
If it is). In addition, the output of the single-type photodetector 12 is S
_When the outputs of _A and the photodetectors 13a and 13b are S _B and S _C , respectively, the output S _A is a + input terminal and the outputs S _B and S _C are −
The differential amplifier 14 input to the input terminal and the output S _B are +
An input terminal and a differential amplifier 15 to which the output S _C is input to the-input terminal are provided. Therefore, the output S _D obtained from the differential amplifier 14 will detect a No. Sashin between a single light detector 12 and the two-divided photodetector 13. Also, output S _E obtained from the differential amplifier 15 will detect a No. Sashin between the two optical detectors 13a, 13b in the two split optical detector 13.

In such a configuration, the response speed of the single type photodetector 12 is now T (A), and the photodetectors 13a and 13 are
The response speeds of b are T (B) and T (C). Therefore,
The output S _{A of the} single photodetector 12 and the split photodetector 13
Output when detecting a No. Sashin between (S _B + S _C), the response speed of the output S _A which is input to the differential amplifier 14 T (A)
Is the output S input from the photodetector 13a, 13b side.
_It is equal to the response speeds T (B) and T (C) of _B and S _C. As a result, the timing of signal input to the differential amplifier 14 is synchronized, so that a timing error is unlikely to occur between signals. In the differential amplifier 15, the photodetectors 13a and 13b are also included.
Response speeds T (B), T of outputs S _B , S _C input from the side
Since (C) is equal, processing can be performed without performing synchronization control. This point can be detected at the same time with respect to the outputs S _D and S _E obtained from the differential amplifiers 14 and 15, so that the complexity of the synchronization process for signal processing is reduced.

Next, the composite type differential detector 1 of the present embodiment
An example of application of No. 1 to the object surface shape detection system will be described with reference to FIG. 2 while referring to FIG. First, the composite type differential detector 11 will be described in more detail. The light receiving surface shapes of the single type photodetector 12 and the two photodetectors 13a and 13b each have an aspect ratio of 1: 2. It has a rectangular shape, and as described above, these areas have the same area. In addition, the longitudinal direction of the single type photodetector 12 and the two photodetectors 13a,
13b are arranged so as to be parallel to each lateral direction,
Moreover, the photodetectors 13a and 13b are juxtaposed so that the longitudinal sides thereof are adjacent to each other. Further, all of these three light receiving surfaces are on the same plane.

For convenience of explanation, the optical axis is the Z axis, the longitudinal direction of the single-type photodetector 12 is the X axis, and the lateral direction is the Y direction.
The composite type differential detector 11 is arranged so as to coincide with the axis, and the perpendicular of the light receiving surface coincides with the Z axis. The origin of such an XYZ coordinate system is the intersection of the longitudinal edge of the single-type photodetector 12 and the dividing line of the two-division type photodetector 13 (FIG. 2B).
reference).

Here, the inclination of the surface of the object 16 is detected from the differential signals of the photodetectors 13a and 13b, and the object is detected from the differential signals of the single type photodetector 12 and the two-division type photodetector 13. The optical system of the object surface shape detection system for detecting the displacement amount of the object 16 in the surface depth direction is configured as shown in FIG. 2A, for example. First, a light source 17, a collimator lens 18, a beam splitter 19, and an objective lens 20 are sequentially arranged on the optical axis of the light source 17 as an illumination system for the measurement surface of the object 16. The objective lens 20 is held by an actuator 21 so as to be slidably displaced in the optical axis direction,
The measurement surface is adjusted so as to be the focal position of the objective lens 20. The reflected light from the measurement surface of the object 16 passes through the objective lens 20 again, and is then reflected by the beam splitter 19 in the direction in which it is branched from the incident light. The composite type differential detector 11 is directly opposed to the optical path reflected by the beam splitter 19 so as to coincide with the optical axis Z. On this reflected light path, a knife edge 22 and a condenser lens 23 for blocking light in the third and fourth quadrants are sequentially interposed. Here, the focus position of the condenser lens 23 is set to be the origin of the composite type differential detector 11.

According to the object surface shape detection system having such a configuration, the X component of the inclination of the measurement surface of the object 16 is detected by the push-pull method from the differential signal (output S _E ) between the photodetectors 13a and 13b. The amount of displacement in the depth direction (Z-axis direction) of the measurement surface obtained is the differential signal between the single photodetector 12 and the two-division photodetector 13 (according to the Foucault method or knife edge method). It is obtained from the output S _D ). Here, such a detection operation is continuously performed while relatively moving the detection optical system in the direction of the measurement surface. At this time, the inclination of the measurement surface and the amount of displacement in the depth direction are measured. As for the signal detection speed of, as described in the basic configuration and operation, the response speed between these signals is uniform, so the problem of delay in signal processing time should be avoided and the complexity of input signal arithmetic processing should be reduced. You can

A second embodiment of the present invention will be described with reference to FIGS. First, the basic configuration and operation of this embodiment will be described with reference to FIGS. 3 and 4.

The composite type differential detector 31 of the present embodiment is constructed on the basis of a slab type optical waveguide device 32, and has a single type photodetector 33 and two split type having two photodetectors 34a and 34b. And a photodetector 34. First, the basic configuration of the slab type optical waveguide device 32 will be described with reference to FIG. The slab type waveguide device 32 includes a buffer layer 36 of a silicon thermal oxide film and a waveguide core layer 3 of a silicon nitride (= Si ₃ N ₄ ) film on a silicon substrate 35.
7. The waveguide clad layer 38 made of a silicon oxynitride (= SiON) film is sequentially laminated. In such a slab type waveguide device 32, a single type photodetector 33 and a two-division type photodetector 34 are formed in a shallow region near the surface of the silicon substrate 35.
A prism coupler 39 having a triangular cross section is bonded to one end side of the waveguide clad layer 38, which is the surface of the slab type waveguide device 32, by an adhesive layer 40a. A gap layer 40b is formed on the surface of the waveguide clad layer 38 to which the prism coupler 39 is not adhered.

Next, the planar structure of the slab type waveguide device 32 will be described with reference to FIG. The prism coupler 39 allows external light to pass through the slab type waveguide device 32.
To couple and guide in the waveguide core layer 37 in
When the optical axis of the guided light is ZZ ', this optical axis ZZ'
On the other hand, there are provided first and second waveguide type reflection concentrators 41 and 42 for taking in the guided light in each of the right and left halves including the optical axis ZZ '. The first waveguide type reflection concentrator 41 that takes in the guided light of the left half as viewed in the waveguiding direction has a reflection boundary surface 41a having a converging curvature due to a parabolic shape, and a reflection boundary surface 41a from this reflection boundary surface 41a. It is formed by a combination with a planar reflection boundary surface 41b that reflects the condensed reflected light. Similarly, the second waveguide type reflection concentrator 42 that takes in the guided light of the right half when viewed in the waveguiding direction also has a reflection boundary surface 42a having a converging curvature due to a parabolic shape, and this reflection boundary surface. 42
a planar reflection boundary surface 4 that reflects the condensed reflected light from a
It is formed by a combination with 2b. However,
The reflection boundary surfaces 41a and 42a may have the same curvature shape, but may have different curvature shapes. In any case, these reflection boundary surfaces 41a, 41b, 42a, 42b are reflection surfaces that are perpendicular to the plane of the slab type waveguide element 32, and the waveguide core layer 37 that sandwiches the reflection surface. The guided light propagating through the waveguide core layer 37 is totally reflected due to the difference in refractive index from the clad layer 38 (or the air layer).

Further, in the plane of the slab type waveguide element 32, a single type photodetector 33 is provided in the vicinity of the condensing position of the condensed reflected light by the first waveguide type reflective condenser 41. Has been. On the other hand, in the plane of the slab type waveguide element 32, a two-division type photodetector 34 is provided in the vicinity of the condensing position of the condensed reflected light by the second waveguide type reflective condenser 42. . The two-division type photodetector 34 is composed of two photodetectors 34a and 34b on the left and right. More specifically, the focal spot of the condensed reflected light of the second waveguide type reflection condenser 42 is arranged so as to be formed on the joint surface between the two photodetectors 34a and 34b.

Here, the light receiving area of the light receiving portion of the single-type photodetector 33 and the light receiving area of each of the light receiving portions of the photodetectors 34a and 34b are such that the area ratio thereof is 1: 1: 1. It is set. Also, these single type photodetectors 33 and 2
The split photodetector 34 is patterned on the silicon substrate 35 using semiconductor technology.

Further, the output of the single type photodetector 33 is S _A ,
Each S _B photodetector 34a, the output of 34b, when the S _C, the output S _A is the positive input terminal, an output S _B, S _C is - a differential amplifier 43 that is input to the input terminal, the output S _B Is a + input terminal and the output S _C is input to a-input terminal
And 4 are provided. Therefore, the output S _D obtained from the differential amplifier 43 will detect the issue between a single light detector 33 and the two-divided photodetector 13. Further, the output S _E obtained from the differential amplifier 44 is the two-division type photodetector 1
Two photodetectors 34a in 3, will <br/> detecting No. Sashin between 34b.

In such a structure, the response speed of the single type photodetector 33 is now T (A), and the photodetectors 34a, 34
The response speeds of b are T (B) and T (C). Therefore,
The output S _{A of the} single type photodetector 33 and the split type photodetector 34
Output when detecting a No. Sashin between (S _B + S _C), the response speed of the output S _A which is input to the differential amplifier 43 T (A)
Is the output S input from the photodetectors 34a, 34b side.
_It is equal to the response speeds T (B) and T (C) of _B and S _C. As a result, the timing of signal input to the differential amplifier 43 is synchronized, so that a timing error is unlikely to occur between signals. In the differential amplifier 44, the photodetectors 34a and 34b are also included.
Response speeds T (B), T of outputs S _B , S _C input from the side
Since (C) is equal, processing can be performed without performing synchronization control. This point can be detected at the same time with respect to the outputs S _D and S _E obtained from the differential amplifiers 43 and 44, so that the complexity of the synchronization process regarding the signal processing is reduced. In addition, since the composite type differential detector 31 is based on the structure of the slab type waveguide device 32, the detection range becomes wider than that in the case of using the bulk type composite type differential detector 11.

The composite differential detector 31 based on the slab type waveguide element 32 thus constructed is, for example,
It is applied to an object surface shape detection system as shown in FIG. The optical system configuration of the object surface shape detection system of the illustrated example is the same as that shown in FIG. 2A, and the same reference numerals are used. In this case, instead of the knife edge 22, the condenser lens 23 and the composite type differential detector 11, the composite type differential detector 31 is arranged so that the prism coupler 39 is located on the reflection optical path of the beam splitter 19. It

According to the object surface shape detection system having such a structure, the Y component of the inclination of the measurement surface of the object 16 is detected by the push-pull method as the single type photodetector 33 and the two-division type photodetector 34.
Is obtained from the differential signal (output S _D ) between the photodetectors 34a and 34b according to the principle of the Foucault method or the knife-edge method. It is obtained from the signal (output S _E ). Here, such a detection operation is continuously performed while relatively moving the detection optical system in the direction of the measurement surface. At this time, the inclination of the measurement surface and the amount of displacement in the depth direction are measured. As for the signal detection speed of, as described in the basic configuration and operation, the response speed between these signals is uniform, so the problem of delay in signal processing time should be avoided and the complexity of input signal arithmetic processing should be reduced. You can In addition, since the composite type differential detector 31 is based on the structure of the slab type waveguide device 32, the detection range becomes wider than that in the case of using the bulk type composite type differential detector 11.

A third embodiment of the present invention will be described with reference to FIG. In this embodiment, the composite type differential detector 31 having the structure shown in FIG. 4 is applied to an optical pickup detection system. Since the structure of this optical pickup detection system can be basically the same as that of the object surface shape detection system shown in FIGS. 2A and 5, the same portions are denoted by the same reference numerals. Here, instead of the object 16, an optical disk 52 having a land 51a and a groove 51b on the surface is used. Then, the composite type differential detector 31 includes the photodetector 3
The focus error signal ΔF is detected from the differential signals (output S _E ) of 4a and 34b, and the track error signal is detected from the differential signal (output S _D ) between the single type photodetector 33 and the two-division type photodetector 34. Detect ΔT. In this case, the actuator 2
1 indicates the objective lens 20 in the Z-axis direction (focus direction) and in the Y-axis direction.
The one that can be displaced in two axial directions, that is, the axial direction (tracking direction) is used.

According to the optical pickup detection system having such a structure, the focus error signal ΔF is obtained from the differential signal (output S _E ) between the photodetectors 34a and 34b by the principle of the Foucault method or the knife edge method. The track error signal ΔT is obtained by the push-pull method using the single-type photodetectors 33 and 2
It is obtained from the differential signal (output S _D ) to and from the split photodetector 34. Here, such a detection operation is continuously performed by rotating the optical disc 52. At this time, the signal detection speeds of the focus error signal ΔF and the track error signal ΔT are as described above. Since the response speeds of these signals are uniform, the problem of delay in signal processing time can be avoided, complexity of the input signal calculation processing can be reduced, and servo control can be stabilized.
In addition, the composite type differential detector 31 uses the slab type waveguide device 3
Since the structure of No. 2 is used as a base, the detection range of the track error signal ΔT becomes wider than that in the case of using the bulk-type composite differential detector 11.

When the composite type differential detector 31 based on the slab type waveguide element 32 is used, the signal light coupling means to the waveguide layer is not limited to the prism coupling method by the prism coupler 39, and for example, An end face optical coupling method, a grating coupling method or the like may be used. However, when the coupled light is wide, the end face coupling method is difficult, and in the case of the grating coupling method, it is necessary to devise the wavelength variation of the incident light and the incident angle tolerance.

[0031]

According to the first aspect of the present invention, regarding the single type photodetector and the two photodetectors in the two-division type photodetector, which compose the composite type differential detector, the light receiving portions of the respective photodetection sections are respectively. By setting the light-receiving area ratio to approximately 1: 1: 1, the response speed characteristics of these detectors were made to substantially match, so there was a delay in response between the signals obtained from these three photodetectors. Therefore, the response characteristics can be made uniform, and the complexity of the synchronization processing between a plurality of types of signals can be reduced.

According to the second aspect of the present invention, the single type photodetector and the two-division type photodetector are formed near the surface of the slab type optical waveguide device on the waveguide substrate side on the waveguide substrate. Therefore, it is possible to easily realize the expansion of the measurement range, which is difficult with the bulk type optical arrangement, and the condensing element can be integrated in the waveguide element, so that the arrangement accuracy can be improved and Arrangement adjustment can be eliminated.

[Brief description of drawings]

FIG. 1 is a plan view showing a basic configuration of a composite type differential detector according to a first embodiment of the present invention.

FIG. 2 shows an example of application to an object surface shape detection system, (a)
Is a configuration diagram of an optical system, and (b) is a front view of the composite type differential detector.

FIG. 3 is a sectional structural view showing a basic configuration of a composite type differential detector according to a second embodiment of the present invention.

FIG. 4 is a plan view thereof.

FIG. 5 is an optical system configuration diagram showing an application example to an object surface shape detection system.

FIG. 6 is an optical system configuration diagram showing an application example to an optical pickup detection system according to a third embodiment of the present invention.

FIG. 7 is a plan view of a waveguide type optical signal detection device showing a conventional example.

[Explanation of symbols]

12 Single photodetector 13 Two-split photodetector 13a, 13b photodetector 32 Slab type optical waveguide device 33 Single photodetector 34 Two-split photodetector 34a, 34b photodetector 35 Waveguide substrate

Claims (2)

(57) [Claims] 1. A single-type photodetector and a two-part photodetector having two photodetectors, the difference between the single-type photodetector and the two-part photodetector. detects the signal, the composite differential detector to detect the issue Sashin between the two optical detectors in the two-divided optical detector, and a light receiving portion of said single photodetector A composite type differential detector characterized in that a ratio of a light receiving area of each of the two photodetectors in the two-division type photodetector to a light receiving portion is set to about 1: 1: 1. 2. The single type photodetector and the two-division type photodetector are formed near the surface of the slab type optical waveguide device on the waveguide layer side on the waveguide substrate. Composite differential detector.